1. Field of the Invention
The present invention relates to a method and a system for regulating the torque-transmitting capacity of a frictionally-engaged torque-transmitting assembly, especially an assembly in the drive train of a motor vehicle.
2. Description of the Related Art
Assemblies that transmit torque in a frictionally-engaged manner in the drive train of a vehicle, such as clutches, including converter lockup clutches in the converter of an automatic transmission, transmissions with endless torque-transmitting means having continuously value transmission ratios (CVT transmissions, friction wheel drives), including brakes, are increasingly automated or operated by their own actuators. The control or the regulation of the frictionally-engaged transmittable torque of the respective assembly should be as low as possible for easing the burden of the actuators, as well as for reasons of low energy consumption and high control or regulation accuracy, but it should be high enough to prevent permanent slippage that can lead to rapid wear or to the destruction of the frictionally-engaged torque-transmitting assembly. Especially because of the latter reason, most of the time an opposite, contact overpressure of the frictionally-engaged torque-transmitting assemblies results. A contact overpressure also generally results because wear of components, settling phenomena, temperature influences, or viscosity-related parameter changes then do not lead to unintended slippage.
One possibility for detecting the slippage condition of two frictionally-engaged torque-transmitting assemblies is known from DE 195 44 061. To detect the adhesion or sliding limits, a pressure-medium-operated actuation element that determines the contact force of the two frictionally-engaged components, is supplied with an actuation pressure that is superimposed on a modulation signal. The gradient of the actuation pressure is correlated with a transmission output shaft speed. The actuation pressure is readjusted In accordance with whether a predetermined correlation value is exceeded or not achieved. It is characteristic of the previously-known method that a sensor must be provided for detecting the modulated pressure and that the correlation calculation can be more difficult by complex phase displacements.
A method for controlling the operation of a frictionally-engaged torque-transmitting assembly is known from DE 199 59 470 A1, in which rotational speed fluctuations of an input element and an output element are correlated with each other without causing the rotational speed fluctuations by modulating the torque-transmitting capacity. One characteristic of that method is that it sweeps a wide frequency range that can be a function of the engine rotational speed, for example, which makes a correlation analysis, such as by means of a Fourier analysis, more difficult.